Blender 2.8 Front and Back Background Images
In Blender 2.8, background is an object.


select one of viewpoint (if you skip this step, the background is always visible regardless of viewport angle)
type Shift-A, and select Image → Background
select an image file


Then, you'll get an object with image. The object has settings for transparency and side, which you want.

So, add two background objects that way, and set the side to Front for one, and to Back for the other.